Non-destructive inspection (NDI) of structures, also referred to as non-destructive testing (NDT), involves thoroughly examining a structure without harming the structure or requiring significant disassembly of the structure. Non-destructive inspection is typically preferred to avoid the schedule, labor, and costs associated with removal of a part for inspection, as well as avoidance of the potential for damaging the structure. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly utilized in the aircraft industry to inspect aircraft structures for any type of internal or external damage to or flaws in the structure. Inspection may be performed during manufacturing of a structure and/or once a structure is in-service. For example, inspection may be required to validate the integrity and fitness of a structure for continued use in manufacturing and future ongoing use in-service. However, access to interior surfaces is often more difficult or impossible without disassembly, such as removing a part for inspection from an aircraft.
Among the structures that are routinely non-destructively tested are composite structures, such as composite sandwich structures and other adhesive bonded panels and assemblies, including, but not limited to, fuselage frames and shear ties, wing stringers, floor beams, flange and radius sections of horizontal stabilizer ribs, and floor stanchions. In this regard, composite structures are commonly used throughout the aircraft industry because of the engineering qualities, design flexibility and low weight of composite structures, such as the stiffness-to-weigh ratio of a composite sandwich structure. As such, it is frequently desirable to inspect composite structures to identify any foreign material or flaws, such as cracks, voids or porosity, which could adversely affect the performance of the composite structure. For example, typical flaws in composite sandwich structures, generally made of one or more layers of lightweight honeycomb or foam core material with composite or metal skins bonded to each side of the core, include disbonds which occur at the interfaces between the core and the skin or between the core and a septum intermediate skin.
Various types of sensors may be utilized to perform non-destructive inspection. One or more sensors may move over the portion of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo (PE), through- or thru-transmission (TT), or shear wave sensor may be utilized to obtain ultrasonic data, such as thickness gauging, detection of laminar defects and porosity, and/or crack detection in the structure. Resonance, pulse echo or mechanical impedance sensors may be utilized to provide indications of voids or porosity, such as in adhesive bond lines of the structure. High resolution inspection of aircraft structure are commonly performed using semi-automated ultrasonic testing (UT) to provide a plan view image of the part or structure under inspection. While solid laminates may be inspected using one-sided pulse echo ultrasonic testing (PEU), composite sandwich structures typically require through-transmission ultrasonic (TTU) testing for high resolution inspection. In through-transmission ultrasonic inspection, ultrasonic sensors such as transducers, or a transducer and a receiver sensor, are positioned facing the other but contacting opposite sides of the structure to be inspected such as opposite surfaces of a composite material. An ultrasonic signal is transmitted by at least one of the transducers, propagated through the structure, and received by the other transducer. Data acquired by sensors, such as TTU transducers, is typically processed by a processing element, and the processed data may be presented to a user via a display.
In order to increase the rate or speed at which the inspection of a structure is conducted, the scanning system may include ultrasonic probes that have arrays of ultrasonic transmitters and receivers or arrays of probes with one or more ultrasonic transmitters and receivers. Typically each “channel” in an array refers to a transducer-receiver pairing and includes a transmit channel to the transducer and a receive channel from the receiver. Generally, the more channels available, the more physical coverage of a part which can be scanned. As such, the inspection of the structure can proceed more rapidly and efficiently, thereby reducing the costs associated with the inspection.
TTU sensors, i.e., TTU transducers and receivers, may be controlled by a variety of systems, including systems which permit multiple TTU transducers and receivers to be used in a single probe, an array of probes, or a combination thereof. The more TTU transducer and receiver pairings, the faster a part may be scanned, presuming the control system can keep up with the data transmissions provided by the TTU transducers and receivers. TTU systems which include numerous TTU transducers and receivers are referred to as having a corresponding number of channels, one channel referring to a transducer-receiver pairing. Multi-channel TTU systems are typically expensive to fabricate, in part because they include a separate RF amplifier and envelope (peak) detector for each receive channel of ultrasound data from a TTU transceiver-receiver pairing. Further, typical multi-channel TTU systems use an individual pulser circuit for each channel, requiring a tremendous amount of space to house and wire numerous channels together. Often multi-channel systems are housed in large racks of electronic components. In addition to expensive costs and large size requirements, maintaining multi-channel systems has typically been problematic and expensive. Typical multi-channel TTU systems may be difficult to troubleshoot because of the number of individual components and extensive wiring required in addition to often obsolete components. Further, typical multi-channel TTU systems are limited to communicating processed signals as 8 bit resolution digital data due to slow processing and/or communication paths and are electronically noisy due to the high number of RF cables which are used to couple the individual components together.
Accordingly, a need exists for an improved system and method for multi-channel non-destructive inspection which provides high data throughput, large dynamic range, and simplicity of supporting electronics.